Interpenetrating LiB/Li₃BN₂ phases enabling stable composite lithium metal anode

Host-less lithium metal anode generally suffers from large volume changes and serious dendrite growth during cycling, which poses challenges for its practical application. Interpenetrating phase composites with continuous architectures offer a solution to enhance mechanical properties of materials. Herein, a robust composite Li anode (LBN) material is fabricated through the metallurgical reaction between Li and hexagonal boron nitride (h-BN) with the formation of interpenetrating LiB/Li₃BN₂ phases. As LiB fibers are anchored by Li₃BN₂ granules, the collapse and slippage of LiB fibers are suppressed whilst the mechanical strength and structural stability of LBN are reinforced. By rolling, ultrathin (15 μm), freestanding, and electrochemically stable LBN foil can be obtained. The LBN anode exhibits a high average Coulombic efficiency of 99.69% (1 mA cm^-2, 3 mAh cm^-2) and a long lifespan of 2500 h (1 mA cm^-2, 1 mAh cm^-2). Notably, the LiCoO₂ (with double-sided load 40 mg cm^-2)|LBN pouch cell can operate over 450 cycles with a capacity retention of 90.1%. The exceptional cycling stability of LBN can be ascribed to the interpenetrating reinforcement architectures and synergistic electronic/ionic conductivity of the LiB/Li₃BN₂ dual-lithiophilic-phases. This work provides a new methodology for thin Li strip processing and reinforced-architecture design, with implications beyond battery applications.